That is a large body of water to try to get control of, I don't have much confidence in electrofishing as a means of adjusting populations, at least as Ive watched it being done once by the local conservation dept, their rattling, clanging, generator powered, aluminum boat they were in had all the fish clearing out of any area way before they got to them, they didn't float enough fish to make any educated guess as to the actual population in the lake, actually Ive landed more on a good day fishing in that lake then they did with their equipment, and never floated one crappie when I have caught a bunch in that particular lake, I think its because they stay out in open, deeper water that they never got any. that being said, I would guess you need to remove a ton of crappie out of your BOW to get some sort of balance, I agree if you could drain it down to a smaller area you will be able to catch and remove a lot easier.
As somebody that has just bought fish to stock a 15 acre lake, I know, killing and starting over in a lake that size is extremely expensive, my wife doesn't know how much I have invested in stocking fish in only a 15 acre lake.